Reactivation of cytomegalovirus (CMV) from latency results in significant morbidity and mortality in immunocompromised solid organ and bone marrow recipients. Despite the ongoing development of effective antiviral agents, and the advent of preemptive therapy, drug-related toxicity and viral gene mutations leading to resistant virus present new clinical challenges, highlighting the need for alternative therapies, potentially aimed at early events in the process of reactivation. This project will focus on the molecular mechanisms of reactivation of CMV from latency, emphasizing the requirement for early triggers of Immediate Early (IE) gene expression, a necessary first step in the viral lytic cycle. The first aim will continue our current investigations into the requirement for TNF signal transduction and downstream activation of NFkB in both HCMV and MCMV IE gene expression in allogeneic grafts transplanted into immunocompetent hosts and investigate other factors likely to contribute to induction of IE gene expression, in an attempt to expand our current knowledge of the molecular mechanisms underlying CMV IE gene expression in vivo. The second aim will be to assemble a molecular definition of the events leading to reactivation of infectious virus from latency in vitro, by characterizing and investigating the molecular requirements for reactivation inferred from the in vivo model. In the third aim, we will test the requirement for the same mechanisms in the production of infectious virus in reactivation from latency in selectively immunocompromised hosts, in an effort to examine the role of the allogeneic immune response in host control of CMV reactivation to infectious virus, to test the hypothesis that TNF induced NFkB activation produced by allogeneic transplantation is required for reactivation of infectious virus in an immunocompromised allograft recipient. In the aggregate, the proposed studies form a logical extension of studies performed in the current grant period and will provide a comprehensive paradigm of central importance to the immunocompromised recipient of an atlograft. A better understanding of the viral and cellular factors responsible for the initial events required for CMV reactivation from latency to productive infection is essential to the development of novel strategies in the prevention of CMV infection and disease.